DAPSUPRSLO

iTrader: (14)

Guys, I've been having discussions lately with a friend who is building a 400" SB2 motor. His heads flow 389 or so CFM with 288 or so cc intake ports. He's showed me some of the 400 plus cfm sb2 stuff and they all seem to be 300+cc. I've been looking at some heavily ported c5-r heads and some new and upcoming heads. They are seeing 393 cfm in a 255 cc port and around 380 out of a 265 cc port. This is quite a big difference in flow compared to volume. My question is do the genn 3 heads (c5r included) have a much shorter intake port hence allowing a 265 cc or 255 cc port to have a similar cross section to a 289 cc sb2 port which is longer? There has got to be something that is hidden hear.

Grimes

iTrader: (3)

I think the shape in general is just more efficient so that you can get better flow out of it. A combination of the cross-section and the way it is routed.

Patrick G

iTrader: (14)

Glad you started mentioning cross sectional area because it's the only way you can compare head to head. An LS1 or LS6 intake runner is going to be shorter than an LS7 head. The LS7/C5R has a higher roof and a shallower valve angle making the port length longer. Even if the cross sectional area was the same as the LS6 head, the port CC VOLUME would be greater by virtue of its longer length.

When comparing LS1/6 heads to LS7/C5R/SB2 heads, it's much better to compare cross sectional area to determine cfm requirements and air speed potential. A 2 sq. inch area port should flow more than a 1.85 sq. inch port.

DAPSUPRSLO

iTrader: (14)

I understand the cross section thing. I'm just curious to the difference in flow numbers verses cross section/volume. For instance, what about the c5-r head verses the sb2. They both are similar valve angle, similar valve size, and similar port location. Wouldn't that mean they have similar port lengths. The c5-r head has got to have a shorter port to maintain the same cross sectional areas and flow as the sb2 port. What are your thoughts.

Patrick G

iTrader: (14)

From what I understand, the intake ports of the C5R/LS7 heads are very similar to the SB2.2 heads in both port volume and length. You may be seeing larger cc volumes on SB2.2 heads because head porters have had lots more years of experience getting big numbers out of them.

DAPSUPRSLO

iTrader: (14)

Well then that means there is something magical about the gen 3 stuff because they are seeing 393 cfm out of a 255 cc port verses 390-415 cfm out of a 295 and up port. If the ports are similar length then the gen 3 is getting much more flow considering the surface area. Maybe the 255 cc port is a misprint or something. Anybody else have any thoughts?

Patrick G

iTrader: (14)

Maybe so, but I find it hard to believe that the intake runner volume of a C5R head flowing 390 is only 255. That would put the cross sectional area awfully small. Could be a misprint. I don't doubt the flow, but I bet the runner volume is larger than 255cc.

SStrokerAce

iTrader: (2)

Remember the formula for finding volume of a cube? L x W x H.... Kinda applies here too.

A C5R port is very similar to a SB2 port, and the fact that the SB2 ports are so big in comparison deals with port length as much as the cross sectional area. A longer port has more volume in it.

The SB2 ports are also used in high RPM motors. A 358 cube 9,500rpm motor needs a lot more cross section to operate properly compared to a 400cube 7,000rpm motor.

Bret

ChucksZ06

iTrader: (9)

I think this is a great question. Isn't the valve angle better on ls7 12 degrees versus 15 for the sb2. That would account for some of the flow efficiency for the Gen111 race heads. As you suggest the length of the port might be part of the answer. A half inch longer port would contain a lot more volume...it is kind of interesting how much discussion there is of port volume in the head when the port of the intake is all part of the whole...I know it is done for comparison purposes but I think it is a little overrated. Take for example the new ls7 with its large ports. It is common thinking that so large a port would have low speed flow problems. Obviously this is not the issue many would suggest or gm would not put this engine into production. I have thought for some time that the thinking from the era of carburators has too much effect on how we think about tuning fuel injected engines and how far we can go with port size, etc.

v8pwr

iTrader: (19)

I don't recall the angles but the SB2.2 is a canted splayed setup like a big block head . This brings up a question I've been wondering , Is there an inline valve head that flows as well as C5R heads ?

Patrick G

iTrader: (14)

The SBC 18 degree Bowtie heads come close, but they still fall short of the C5R heads. Even the badass AFR, Brodix, and Pro-Action heads for the SBC are not any better than the C5R heads (when all are ported to their max potential).

Again, you're going to find though, there's a lot more porting experience on the SBC stuff than the Gen III stuff so you'll probably be seeing better flow numbers on the SBC stuff for a few more years even though the C5R heads have equal to greater POTENTIAL.

SStrokerAce

iTrader: (2)

SB2 is 11° x 4° on the intake and 8° on the exhaust.

C5R is 11° inline, the C5R is one hell of a bad *** inline head. The ET performance stuff that's comming out should be pretty kick *** as well.

Bret

Cary@Perf-Induction

iTrader: (1)

not a misprint,
our c5r is 255 cc, and has an average cross section of 2.97 sq inches, 2.180 valve and a 50 degree seat. peak flow is 393 cfm. with a 55 degree seat it was 404 cfm avg. our new ETP "c5r" stle head head has a higher port location than the gm c5r head, thus has lenghtened the port center length by .375. the c5r is not equally compared to the sb2 mostly because of the canted valve arrangement and the int valve is pulled far back from the cylinder centerline, that will shorten the port by .500 over the c5r. our cathederal port 265 cc intake runner is only .100 shorter than the c5r and outflows the ls7 head at equal port volumes with a .100 smaller valve and .125 smaller bore. So even so that some things are hard to believe, they can be true. Give things another 2or3 years and watch how things evolve. I saw it in the ford world, and you will se a lot of numbers popping up that don't seem possile.

Patrick G

iTrader: (14)

Awesome. Like I said, I didn't doubt the flow numbers...it's just amazing to see them out of such a small cross sectional area. Well done!